In this module, we learned about G protein function as a binary switch.  G proteins have an intrinsic enzymatic ability to hydrolyze GTP to GDP + Pi.  Why, then, would a cell need additional G protein controls like GEFs or GAPs?  What advantages do you see this providing?

Suppose a new patient, patient HLU, presents with fatigue and failure to thrive within a few days.  Upon further investigation, it is discovered that HLU has hypoglycemia between feedings and lactic acidosis right after feeding.  In addition, isoelectric focusing of the protein transferrin from his bloodstream, transferrin being a heavily glycosylated protein, reveals that HLU has erroneous N-linked glycosylation of transferrin.  Biosynthesis of N-linked glycosylated glycoproteins require UDP-glucose and UDP-galactose for construction of the oligosaccharide that gets added to the protein in the endoplasmic reticulum.  Muscle biopsy later in life reveals that he has a glycogen storage disease – there are excess amounts of normally structured glycogen in muscle cells.    Early in life, he was subjected to the Beutler test and misdiagnosed with galactosemia because NADPH levels did not increase as readily as wild type patient upon administration of galactose.  Which enzyme is deficient in…

Two protein kinases, barley kinase and hops kinase, function sequentially in an intracellular signaling pathway. If either kinase contains a mutation that permanently inactivates it, no response is seen in cells when an extracellular signal is received. A mutation that permanently activates barley results in a response even when there is no extracellular signal. You characterize a double mutant in which hops has the inactivating mutation and barley has the activating mutation. You observe that a response is seen in the double mutants even in the absence of an extracellular signal. In the normal signaling pathway, does barley phosphorylate hops or does hops phosphorylate barley? Briefly explain your answer.

You are in a research lab studying the function of the mutated form of a receptor called Protein X, which results in disruptive symptoms in human patients: extreme fatigue, low blood pressure, and dizziness among other symptoms that may be affecting the reproductive system. From detailed genetic studies, you have found that there is a mutation in the region where the Nuclear Localization Signal (NLS) of Protein X is, which may account for the symptoms seen in patients. What kind of receptor is Protein X most likely to be? Select one: O a. Steroid Family Receptor O b. GPCR Growth Hormone Receptor O d. Thyroid Hormone Receptor